1. Technical Field
The disclosure relates to a gain adjustment device and a method thereof, and more particularly to an automatic gain adjustment device and a method thereof.
2. Related Art
Generally, an audio amplifier is employed to enable an audio system to output an audio signal with a large power. The audio amplifier requires a higher voltage in order to provide a larger output power. It is assumed that the voltage of an original audio signal is AVDD, and the voltage of an amplified audio signal output by the amplifier is SPKVDD, so that the original audio signal must be multiplied with a gain ratio (SPKVDD/AVDD), in order to avoid distortion or problems relating to an incorrect level of the audio signal. Conventionally, the gain ratio is set as a parameter, i.e., the gain ratio is a constant value, which may not be altered arbitrarily.
However, the voltage (SPKVDD) of the amplified audio signal output by the audio system does not always maintain a constant value. For example, in an ordinary handheld device, the power source of the audio amplifier is usually coupled to an output of the cell, and the voltage of the cell somewhat varies according to the electrical charge of the cell. Alternatively, when the handheld device is connected to a charger, the change of the power source system may also cause alterations of the SPKVDD. At this time, when the SPKVDD changes but the gain ratio fails to be adjusted accordingly, distortion and problems relating to an incorrect level of the audio signal may occur.
Therefore, a solution is needed urgently to eliminate the problems caused by the gain ratio in the audio system.